Electronic air cleaners have been used in the restaurant industry for many years. Electronic air cleaners have been used both to purify outside air drawn into the restaurant, and to clean exhaust cooking air so that it can be discharged outdoors. However, it has been difficult to remove all particles, oil and grease droplets, vapors and odors from commercial cooking effluent so that the exhaust can be returned directly to the room.
Conventional hood filtration systems used in commercial kitchens employ electronic air cleaners for removal of particles from the air. These electronic air cleaners do not adequately remove vapor and odors. The conventional electronic air cleaners use a positive corona (electrodes with positive polarity) to minimize ozone production.
Attempts have been made to remove vapors and odor by placing charcoal granular beds downstream from the electronic air cleaner. The charcoal beds have not proven effective in odor removal, and instead emit rancid odors when not frequently replaced. Other kitchen hood systems employ baffles and chemical baths to remove grease, vapor and odors. These systems require high maintenance, and have not proven effective in removing odors. Absent frequent maintenance, the performance of these hood systems deteriorates rapidly.